1. Field of the Invention
This invention relates to pneumatic vehicle wheels and the means for improving the behavior of such wheels under conditions of vibration caused by an uneven road surface.
2. Description of the Prior Art
Most modern means of transportation are equipped with wheels having pneumatic tires containing compressed gas (air). Besides the main task--to insure reliable grip with the road surface--pneumatic tires also create a resilient connection between the vehicle and the road surface in which the resilience depends mainly on the pressure of air in the tire. The damping effect of this resilient connection is usually very small and is determined mainly by the damping characteristics of the tire material. As a result, when disturbances from the road have frequencies sufficiently higher than the natural frequency of the vehicle/tire system the tires behave as vibration dampers, but for vibration frequencies close to said natural frequencies, tires tend to worsen the vibration effect on the vehicle. If the vehicle has a suspension system, the harmful increases of the vibration effect on the vehicle when the frequency is near the natural frequency of the vehicle/tire system are reduced, because the natural frequency of the suspension system is usually much lower than that of the tire itself. However, even a limited increase of the vibration level at the tires's natural frequency is very unpleasant and in many cases can force the designer to lower the natural frequency of the suspension system. Especially bad consequences for the strength of the vehicle and its component units, passenger comfort, cargo conditions, etc., are encountered in cases when the tires are the sole resilient element, such as in wheeled tractors or bicycles. Using the tires themselves as part of the suspension system will reduce the effects of vibration on the vehicle. This can be accomplished by providing a means by which the pressure in the tire changes in response to external disturbances, and means by which a part of vibrational energy is dissipated in the form of heat, thereby damping road shocks.
Some existing systems for altering tire pressure are intended to merely replace air lost in the normal course of operation or to allow different pressures for on or off-road conditions. There are also systems directed, as is the present invention, toward dynamically changing the pressure during operation and in response to road conditions. One of these systems (U.S. Pat. No. 2,216,854 to R. S. Sanford) involves chassismounted pressure tanks connected through the axle to the tires by a rotational coupling. A valve system senses pressure changes in the tires and constantly vents excess pressure to the atmosphere and replaces lost pressure from the pressure tanks. The inherent complexity and cost of the rotational couplings and the valving system, along with the requirement to refill the pressure tanks when depleted, make this design unattractive.
A simplified system, disclosed in U.S. Pat. No. 2,690,779 to J. P. Rust, approaches the problem by placing, inside the tire cavity itself, an extra chamber that will assume its share of the pressure increase, via a valve that is substantially one-way, when the tire is compressed, and that then maintains its high pressure when the tire assumes its normal expanded shape, bleeding air back to the tire cavity at a rate that gradually increases the tire pressure to normal levels. The valving required within the tire, however, still presents a complexity problem, and it could produce rotational imbalance in the wheel.